Real Dictionary

orthodox
If you describe someone as orthodox, you mean that they hold the older and more traditional ideas of their religion or party.
adjective: Orthodox beliefs, methods, or systems are ones which are accepted or used by most people.

orthodox in American English
conforming to the usual beliefs or established doctrines, as in religion, politics, etc.; approved or conventional [orthodox ideas]
adjective: of, pertaining to, or conforming to the approved form of any doctrine, philosophy, ideology, etc

orthodox in British English
adjective: conforming with established or accepted standards, as in religion, behaviour, or attitudes
adjective: of or relating to the Orthodox Church of the East